16 MICROBES, FERMENTS, AND MOULDS. 
of wheat, but only upon the leaves of another plant, 
the barberry. 
Borne by the dew or by a drop of rain on to the 
young leaves of the barberry, the teleutospores germi- 
nate, and form reddish-brown patches which’ affect 
both sides of the leaf. On its lower surface the 
spores are smaller, and are termed spermata; their 
function is not thoroughly understood. The larger 
spores on the upper surface are called acidiospores 
(Fig. 6), and with these we are more concerned, since 
Fig. 6-—Section of a barberry-leaf bearing two cecidiospores, more or less developed, 
of Puccinia graminis (much magnified), 
they are destined to return to the wheat, rye, or other 
grasses, in order to reproduce the original rust. 
When they are placed on a blade of one or 
other of these grasses, the cecidiospores germinate at 
once, and it is soon covered with patches resembling 
those of the preceding year; when these patches are 
numerous, they dry up the blade and destroy the ear. 
Hay and straw affected by rust should never be 
given to animals as food, since such food may produce 
disease. 
Thus it appears that Puccinia graminis presents 
the phenomenon of alternation of generations; that is, 
